1. Field of the Invention
The present invention relates to a fluorescent lamp. More specifically, the present invention relates to a fluorescent lamp having a reduced adverse effect on the environment by improving the glass bulb material and the arrangement to provide an electrode to the fluorescent lamp.
2. Description of the Prior Art
A fluorescent lamp generally has the following configuration. As shown in FIG. 5, a conventional fluorescent lamp includes a cylindrical glass bulb 33 whose inner surface is coated with a fluorescent substance 37. The glass bulb 33 is sealed with stems at both ends of the glass bulb 33 (FIG. 5 shows only one end of the glass bulb 33). The stem includes a flare 32, an exhaust tube 34, lead wires 35 and a filament coil 36. The two lead wires 35 are connected to the ends of the filament coil 36. The glass bulb is evacuated to a vacuum, and mercury and a rare gas are injected through the exhaust tube. Then, the exhaust tube 34 is sealed. A lamp base 38 is attached to the end of the glass bulb 33 with cement 39. The lead wires 35 are connected to electrodes terminal pins 31 provided in the lamp base 38.
The glass bulb 33 is formed of a soda-lime glass comprising 10 to 20 wt % of sodium oxide because of its low cost and easy processing. Generally, lead glass containing 4 to 28 wt % of lead oxide is used as a glass material for the stem including the exhaust tube and the flare because it is handled easily in a heating process. Furthermore, the lamp base 38 is formed of aluminum or plastic such as polycarbonate. The cement 39 is formed by using an organic solvent such as phenol.
On the other hand, great attention has been given to environmental issues recently. In response to this tendency, in the field of fluorescent lamps, various efforts to reduce adverse effects on the environment have been undertaken. Recycling of waste lamps, reduction of environmental contaminants and upgrading of the workplace are examples of such efforts.
A variety of approaches have been proposed to pursue recycling of fluorescent lamps so that mercury, soda-lime glass and lead glass can be reused by a recycling treatment. However, there still remains a problem in sorting glass by type, so that the glass materials have not completely been reused yet. As for lamp bases, the cost of recycling is unattractively high, and therefore, waste lamp bases are buried in the earth at present.
The most problematic contaminants are mercury and lead. To tackle problems of mercury, a method for sealing up mercury has been changed. More specifically, a liquid mercury was sealed up by dropping before, whereas other methods associated with use of capsules, alloy, or amalgam are used at present. Thus, the amount of mercury contained is reduced, and the workplace is improved.
However, mercury is contained in a lamp in an amount larger than the amount theoretically necessary for the fluorescent lamp to light.
A larger amount of mercury is necessary partly because mercury is consumed by soda-lime glass generally used for a glass bulb. When the lamp including a glass bulb formed of soda-lime glass lights on, sodium ions in the soda-lime glass diffuse to the surface of the glass bulb while the lamp is on. The diffused sodium ions react with mercury vapor. Alternatively, mercury is fixed to voids formed as a result of the diffusion of sodium ions. Such mercury no longer contributes to discharge. These phenomena consume mercury, and therefore a superfluous amount of mercury, which is larger than an amount necessary for the glow of the lamp, is required to be sealed up in the lamp.
As for lead, a variety of glasses that contain less lead or do not contain lead have been proposed. However, any proposed glasses have drawbacks in their characteristics. Therefore, a glass containing a large amount of lead oxide is still used at present. When the glass containing a large amount of lead oxide is heated at a high temperature during the production steps for a lamp, toxic lead oxide is scattered and evaporated into the air. This fact may cause a large adverse effect on the workers or the environment. Therefore, a large financial investment is required to counter these problems so that the adverse effect on the workers or the environment can be reduced.
As described above, the lamp base and the lead glass in the conventional fluorescent lamp cause environmental problems. More specifically, the lamp base is buried in the earth after the lamp is disposed of The lead glass releases toxic lead oxide, which requires a large financial investment to prevent this problem. In addition, the lead glass is hardly recycled. Furthermore, the use of soda-lime glass for a fluorescent lamp prevents a reduction of the amount of mercury to be sealed up in the fluorescent lamp.